German Patent Application 196 01 791 describes a sensor chip having a sensor area composed of a frame element, a recess, and a membrane, for example. An unwanted influence on the measuring signal of the sensor chip in the sensor area may occur repeatedly due to contamination, e.g., oil, to which the sensor chip is exposed. Contamination with oil in the sensor area or in the immediate area around the sensor area alters the thermal conductivity at the surface of the sensor chip and thus affects the measuring signal. In addition, oil deposited on the sensor chip forms an adhesive for particles contained in a flowing medium. These trapped particles further increase the unfavorable effect.
U.S. Pat. No. 5,705,745 describes a sensor chip having a membrane on which are arranged temperature resistors and heating resistors, the membrane being surrounded by a thermally conductive element, which may also be U-shaped. The thermally conductive element is not heated. The thermally conductive element is also situated at least partially in the area of the membrane.
U.S. Pat. No. 4,888,988 describes a sensor chip having a membrane, a metallic conductor being situated around the is the common grounded neutral conductor of the measuring arrangement on the sensor chip. The cross section of this grounded neutral conductor has even been increased selectively to prevent an increase in temperature. An elevated temperature of the grounded neutral conductor would also have an extremely deleterious effect on the measurement according to this method.
German Patent Application 198 01 484 describes a sensor chip having a membrane, electric conductors being situated around the membrane with an electric current flowing through them. These conductors are temperature sensors which are used for the measurement method and/or the measurement procedure.
German Patent Application 2 900 210 and U.S. Pat. No. 4,294,114 describe a sensor chip having a temperature-dependent resistor on a carrier, another resistor directly adjacent to the temperature-dependent resistor also being applied to the carrier.
German Patent Application 4 219 454 and U.S. Pat. No. 5,404,753 describe a sensor chip having a reference temperature sensor at a distance from a sensor area.
German Patent Application 3 135 793 and U.S. Pat. No. 4,468,963 describe a sensor chip having another resistor upstream and/or downstream from the sensor resistor, but the additional resistor influences the measuring signal.